Plywood generally holds nails and screws better than oriented strand board. In some areas OSB is not allowed as roof sheeting because of nail pullout problems. Plywood also holds up better if it gets wet.

However, OSB is usually less expensive and is widely used where nail pullout is not a problem and there is a minimal chance of it getting wet. If you have any doubts about which one to use, find a scrap piece of each and pound a few nails in, pull them out, and decide for yourself which will work best for your application.

When framing a house, should I use 2-by-4s or 2-by-6s?

Standard framing is with 2-by-4s, which are less expensive than 2-by-6s. But 2-by-4s must be spaced 16 inches on center while 2-by-6s often can be spaced 24 inches on center, so you use a few less. Additionally, 2-by-6s allow you to place higher R-value insulation in the walls, which will reduce your heating and cooling costs. However, there are some hidden costs to using 2-by-6 framing, such as wider doorframes and wider window sashes.